A milling machine is a power-driven machine used for the shaping of parts. In its simplest form, a milling machine consists of a rotating cutter and a workspace. A workpiece is placed on and/or secured to the workspace and the rotating cutter is guided to remove unwanted material from the workpiece to shape the desired part. To accomplish this, either the rotating cutter is moved while the table is stationary, the table is moved while the rotating cutter is stationary, or both the rotating cutter and the table move to allow the rotating cutter to remove material.
Early milling machines were operated manually which allowed production of parts with limited complexity. Computers then spurred the development of computer numerical control (CNC) machines. CNC milling machines allow for the production of extremely complex parts. The more advanced CNC milling-machines add one or more additional axes in addition to the three standard axes (XYZ). The C axis allows the workpiece to be rotated. The B-axis controls the tilt of the tool itself. When all of these axes are used in conjunction with each other, extremely complicated geometries, even organic geometries, such as a human head, can be made with relative ease with these machines.
Milling machines are used to manufacture parts like aircraft and ship components. Large milling machines may be massive enough to require their own building. These massive milling machines are very expensive as are the parts produced by them. Due to the high costs involved, little competition exists for the owners of these mammoth machines.
One drawback for large milling machines is that the further the cutting tool gets away from the center of the workpiece, the less accurate the cutting becomes. This decrease in accuracy may be described and visualized as a “bow-tie” template. A variety of factors contribute to the inaccuracies realized as a cutting tool moves further from the center of the workpiece. These factors include environmental variations (e.g., thermal variations), and structural variations in both the workpiece and the milling machine. These variations result in expansion and/or contraction of the workpiece and the milling machine.
A fiducial calibration system is disclosed in U.S. Pat. Nos. 6,782,596 and 7,065,851 which are herein incorporated by reference. The use of fiducials has improved accuracy in the production of parts. However, this has accomplished nothing in reducing the size of gargantuan milling machines required to mill them. In the industry today, a milling machine must be as large as the largest dimension of the part it is manufacturing. For example, if a part's dimensions are 10×3×1 meters, it will require a milling machine that can traverse the entire 10 meters. It would be a great benefit to the industry if a milling machine was required to accommodate only the second largest dimension of a three dimensional workpiece or part. Using the example from above, a milling machine would only be required to accommodate the 3 meter dimension instead of the 10 meter dimension. However, size is not the only relevant factor. A milling machine which may accommodate a part whose dimensions are 1.0×0.1×0.05 meters would be required to accommodate the 0.1 meter dimension instead of the 1.0 meter dimension. That translates to a machine that may sit on a tabletop instead of a larger machine that must sit on the floor.
The benefits would include cost savings for the manufacturer from constructing smaller milling machines, cost savings to the consumer from constructing smaller milling machines and increased competition between part manufacturers.
Hence, there exists an unsatisfied need for a more accurate and less expensive method for the manufacture of large parts on small machines through the use of fiducial calibration methods.